The present invention relates generally to a compact blowout preventer used in the oil and gas industry. Specifically, the invention relates to a compact blowout preventer featuring a nested cylinder actuator and ram system wherein the overall outer diameter of the device is reduced by combining the ram and actuator cylinder, and increasing the actuator piston area with a second nested cylinder and piston.
Blowout preventers are used in the subsea oil and gas production industry to seal the well bore in the event of a blowout. The blowout preventer (“BOP”) may be mounted on a subsea wellhead or christmas tree or located on a surface vessel and connected to the subsea wellhead or christmas tree via a riser. During installation and workover operations, a workover string, such as drill pipe, wireline or coiled tubing, may be lowered through the BOP and into the well bore. In the event of a blowout during any of these operations, the BOP must therefore be able to seal the well bore in the presence of the workover string.
Typical ram-type BOP's normally include an elongated housing, a BOP bore which extends axially through the housing and a pair of opposing BOP rams which are movable laterally across the BOP bore toward and away from each other. The BOP rams are normally actuated by respective pistons which move perpendicular to the BOP bore and are therefore mounted in ram housings which extend laterally from the BOP housing. As a result, these types of BOP's tend to be quite large. For example, one known prior art 10,000 psi surface BOP having a 13⅝″ BOP bore comprises an envelope outer diameter of about 120 inches. Such BOP's require that the surface vessel be equipped with a correspondingly large rotary table to enable the BOP to pass through. However, surface vessels of this size are very expensive to operate.